1. Field of the Invention
The present invention relates to a vehicle exterior monitoring device and a vehicle exterior monitoring method for monitoring vehicle exterior condition based on distribution of distances of three-dimensional objects outside of a subject vehicle to the subject vehicle.
2. Description of Related Art
There have been known technologies for detecting a three-dimensional object such as a vehicle located ahead of a subject vehicle (such as a preceding vehicle and a vehicle stopping ahead) and an obstacle, and controlling to avoid collision with the detected three-dimensional object and keeping the inter-vehicle distance to the preceding vehicle at a safe distance (for example, see Japanese Patent No. 3349060 and Japanese Patent Application Laid-Open (JP-A) No. 10-283461).
In such technologies, a relative three-dimensional position (position information) of a three-dimensional object located ahead including a relative distance to the subject vehicle is derived by using a distance sensor or the like to identify the object. However, the distance sensor itself for detecting a relative distance generally cannot recognize what object the detected part belongs to. Accordingly, the three-dimensional position of the detected part is derived independently in units of detection resolution in a detected area instead of in units of an object. Therefore, a process will be required that extracts and groups positional information of adjacent three-dimensional positions in units of detection resolution, and identifies the positional information group as a three-dimensional object.
With the technologies of Japanese Patent No. 3349060 and JP-A No. 10-283461 mentioned above, a detected region is first divided into a plurality of strip-shaped divided regions, and for each of the divided regions, detected position information is statistically processed to obtain distance distribution, and a relative distance corresponding to a peak in the distance distribution is obtained as a representative value (representative distance) in the divided region. Then, the representative distances are compared to each other to be grouped as a three-dimensional object.
In the grouping process performed in the technologies of Japanese Patent No. 3349060 and JP-A No. 10-283461 described above, the region is divided into strip-shaped divided regions extending in the vertical direction because a rearmost preceding vehicle on a road can be uniquely identified in a divided region. In addition, the relative distance corresponding to a peak in the distance distribution is used as the representative distance so as to exclude unexpected position information as a result of false detection.
However, a plurality of relative distances may be detected in a strip-shaped region for one integrated three-dimensional object. For example, in a vehicle such as a truck, relative distances of a cabin part and a rear side of a cargo bed to the subject vehicle are different, and accordingly, two relative distances of the cabin part and the rear side of the cargo bed are mainly detected in the distance distribution within the strip-shaped region.
In this case, since the relative distance corresponding to a peak in the distance distribution of a divided region is the representative distance in the technologies of Japanese Patent No. 3349060 and JP-A No. 10-283461 mentioned above, the distance distribution may change depending on a detected condition such as areas covered by the cabin part and the rear side of the cargo bed and the number of parts that can be detected.
The relative distance corresponding to a peak may change with such change in the distance distribution, and it may thus be difficult to specify what part has the relative distance corresponding to the representative distance. Then, the cabin part and the rear side of the cargo bed cannot be grouped as one three-dimensional object and the three-dimensional object may not be correctly recognized. For example, when the relative distance of the cabin part and the relative distance of the rear side of the cargo bed are detected successively in time as the relative distance to the three-dimensional object, this may lead to the following situation. The subject vehicle may react faithfully to the change in the relative distance of the preceding vehicle through control (cruise control) for keeping the inter-vehicle distance to the preceding vehicle to be safe, and the passengers may feel uncomfortable with the acceleration or deceleration of the subject vehicle.